Method and device for automatic control of an aircraft deceleration in running phase

ABSTRACT

The invention relates to a system to control the deceleration of an aircraft during the taxiing phase on a landing strip, the system comprising:  
     acquisition means ( 100 ) of the current position of the aircraft on the strip,  
     acquisition means ( 100 ) of the current speed of the aircraft on the strip,  
     calculation means ( 102 ), receiving position and speed values from the acquisition means, to define, as a function of the desired final speed of the aircraft at the so-called final position on the strip, a deceleration set-point modification time, after the current time, and a new deceleration set-point to apply from the modification time, to reach the final position at the desired speed.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority based on International PatentApplication No. PCT/FR01/03923, entitled “Method And system For TheAutomatic Control Of Aircraft Deceleration During The Taxiing Phase” byFabrice Villaume, which claims priority of French application no.00/16147, filed on Dec. 12, 2000, and which was not published inEnglish.”

FIELD OF THE INVENTION

[0002] The present invention relates to a method and system for theautomatic control of the deceleration of an aircraft during the taxiingphase.

[0003] A distinction is generally made, when an aircraft is beinglanded, between three steps which are: the approach phase, impact andthe taxiing phase of the aircraft on a landing strip. The taxiing phaseis used to decelerate the aircraft, so as to enable it to turn into anexit junction of the landing strip, thus freeing said strip.

[0004] Due to chronic congestion in airports, and the costs associatedwith the use of landing strips, efforts have been concentrated onreducing the time during which they are occupied by aircraft.

STATE OF THE RELATED ART

[0005] At the present time, a number of large carrier aircraft areequipped with an automatic braking system which makes it possible to seta predetermined deceleration set-point. Generally, three or five brakinglevels are provided. These levels are, for example, “low”, “medium”, and“high”. The high braking level is not used under normal conditions, butonly in the event of emergency braking. The braking levels arepre-defined and do not account for the strip condition and layout orweather conditions.

[0006] The use of predetermined braking set-points does not make itpossible to optimise the strip occupation time on landing.

[0007] Through the document EP A 0 895 929, a perfected automaticbraking system is also known which accounts for the distance separatingthe point of impact of the aircraft on the strip and the parking or exitposition. It also accounts for the current speed of the aircraft and itsfinal speed (which may be zero). According to this document, adeceleration given by the following formula is applied to the aircraft:$\begin{matrix}{\frac{V_{final}^{2} - V^{2}}{2L}} & (1)\end{matrix}$

[0008] In this expression, V_(final), V and L respectively refer to thefinal speed of the aircraft at the end of the strip, the current speedof the aircraft and the distance separating the final position from theaircraft's current position.

[0009] A more detailed description of the calculation of thedeceleration given by formula 1 can be found in the document referencedabove.

[0010] The automatic braking system makes it possible, at least in anumber of cases, to reduce the landing strip occupation time compared tosystems with constant and predetermined braking levels.

[0011] The aim of the present invention is to propose a decelerationcontrol method and system making it possible to optimise braking evenfurther and reducing landing strip occupation time even further.

[0012] A further aim is to propose such a method and such a systemcapable of being installed or being used on aircraft not initiallyequipped.

DESCRIPTION OF THE INVENTION

[0013] To achieve these aims, the invention more specifically relates toa system to control the deceleration of an aircraft during the taxiingphase on a landing strip, the system comprising:

[0014] acquisition means of the current (instantaneous) position of theaircraft on the strip,

[0015] acquisition means of the current (instantaneous) speed of theaircraft on the strip,

[0016] calculation means (102), receiving position and speed values fromthe acquisition means, to define, as a function of the desired finalspeed of the aircraft at the so-called final position on the strip, adeceleration set-point modification time, after the current time, and anew deceleration set-point to apply from the modification time, to reachthe final position at the desired speed.

[0017] The above-mentioned final position is, for example, the positionof an exit junction of the landing strip. The aircraft must reach thisposition at a sufficiently low final speed to leave the strip incomplete safety. The desired value of the final speed along with thefinal position are data that can be determined beforehand and saved in amemory of the calculation means, for example.

[0018] As the deceleration value modification time is after theso-called current time, the aircraft covers a specific distance beforethe new deceleration set-point is applied.

[0019] At the moment of impact, i.e. when the current time coincideswith the landing gear coming into contact with the strip, no taxiingphase deceleration set-point is applied to the aircraft. If applicable,a predetermined low deceleration set-point may be applied. Therefore,the aircraft only undergoes, initially, low deceleration correspondingto the aerodynamic braking or a predetermined set-point braking, ifapplicable. In this way, it covers an initial portion of the landingstrip at a high speed, at least until the deceleration set-pointmodification time. From this time, the braking means are reallyimplemented. More specifically, the braking means are implemented to theextent required to reach a desired speed at the set final point. Bydelaying the deceleration set-point modification time, it is possible tocover a greater portion of the strip at a higher speed and thereforereduce the strip occupation time. The deceleration of the aircraftincreases according to the distance of the deceleration set-pointmodification time(s) with respect to the impact time.

[0020] In one particular embodiment of the invention, the calculationmeans may be equipped with a neural network type computer, capable,during a learning phase, to find a balance between an optimal reductionof the taxiing time and safety and comfort requirements for aircraftpassengers.

[0021] The term aircraft braking means refers to any equipment intendedto decelerate the aircraft during the taxiing phase. These means maycomprise disk brakes acting on the wheels of the landing gear orpossibly so-called propeller thrust inversion devices. The braking meansmay also comprise other aerodynamic braking devices such as groundspoilers or a tail parachute.

[0022] The deceleration value to be applied to the aircraft from theset-point modification time may be obtained, for example, according to alaw comparable to that given by equation 1. However, in this equation, Vis no longer the current speed of the aircraft, but the estimated speedat the set-point modification time, and L is no longer the distanceseparating the current position from the final position, but thedistance separating the estimated position at the set-point modificationtime and the final position.

[0023] According to one particular aspect of the invention, the controlsystem may comprise continuous acquisition means of the current positionand current speed of the aircraft, and continuous calculation means ofnew deceleration set-points.

[0024] By means of the continuous calculation of new decelerationset-points and, if applicable, new set-point modification times, it ispossible, after the first set-point modification time, to correct thedeceleration or adjust it so as to reach the final position at a speedcorresponding as precisely as possible to the desired speed,independently of the weather condition and independently of thecondition of the landing strip.

[0025] According to another particular aspect of the invention, thecurrent position acquisition means may comprise a GPS (globalpositioning system) type system. In addition, the current speedacquisition means may comprise an IRS (internal reference system) typespeed measurement system specific to the aircraft.

[0026] The invention also relates to braking equipment for an aircraftliable to land on a landing strip and equipped with a decelerationcontrol system as described above.

[0027] The equipment may also comprise an anti-blocking system connectedbetween the deceleration control system and the brakes acting on thewheels of the aircraft, to prevent any blocking of wheels.

[0028] Finally, the invention relates to a method to control thedeceleration of an aircraft running on a landing strip, between at leasta current position of the aircraft occupied at a current time, at whichsaid aircraft has a current speed, and a final position at which theaircraft must have a determined final position, wherein a decelerationset-point modification time, after the current time, and a newdeceleration set-point applied from said set-point modification time,are determined as a function of the current position, the current speedand the final speed, in order to reach the final position at thedetermined speed. The final position is, for example, an exit junctionof the landing strip.

[0029] Other characteristics and advantages of the invention will emergefrom the following description, with reference to the appended figures.This description is given for purely illustrative purposes and is notexhaustive.

BRIEF DESCRIPTION OF FIGURES

[0030]FIG. 1 is a schematic representation of a landing strip showingthe main parameters taken into account for the calculation of thedeceleration of an aircraft according to the invention.

[0031]FIG. 2 is a graph showing, as a function of time, measured fromthe impact of an aircraft onto the strip, the variation of adeceleration set-point applied to an aircraft braking system accordingto the invention.

[0032]FIG. 3 is a graph showing the variation of the aircraft speed onthe landing strip, as a function of time, accounting for thedeceleration set-point in FIG. 2.

[0033]FIG. 4 is a schematic representation of braking equipment showingthe main components of a deceleration control system according to theinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0034]FIG. 1 schematically represents a landing strip 10 approached byan aircraft in the direction indicated by an arrow after an approachphase.

[0035] The deceleration of the aircraft during the approach phase doesnot come within the scope of the invention. The aircraft decelerationcontrol method, according to the invention, relates to the taxiing phasewhich takes place on the strip 10 from an impact point 14 in an impactzone, up to a point 16 a or 16 b from which the aircraft starts to leavethe strip 10.

[0036] In the example in the figure, the strip comprises two exitjunctions 18 a and 18 b that an aircraft can take by deviating itstrajectory from points 16 a and 16 b, respectively. These points arehereafter referred to more simply as “exit points”.

[0037] The choice of taking the first or second exit junctionessentially depends on the type of aircraft, and possibly the landingconditions. The first exit 18 a will be considered to have been taken.

[0038] The aircraft reaches the impact point 14 of the linear coordinateX at a speed V. Its deceleration must be sufficiently high for its finalspeed at the exit point 16 a to have a predetermined value V_(final),adapted to the change of direction of its trajectory in the exitjunction 18 a. To change from the initial speed to the final speed, thelength L of the taxiing path is L=X_(final)−X where X_(final) is thelinear coordinate of the exit point.

[0039] The impact position and speed coordinates X, V are acquired byequipment, onboard or not, known to those skilled in the art. Itconsists of, for example, GPS (global positioning system), IRS (internalreference system) type equipment, accelerometers, telemeters, etc. It isimportant to note that the impact position and speed parameters X and Vmay be objective parameters effectively measured at the impact time, butmay also be estimated parameters calculated on the basis of the speed,position and possibly the deceleration of the aircraft before impact onthe strip, or possibly after impact.

[0040] The position and the speed of the aircraft at impact mayrepresent the “current” position and the “current” speed within thescope of the invention, to calculate the deceleration set-point. Also inrelation to this point, it is important to note that a position occupiedby the aircraft and a speed of the aircraft, after those of the impact,may also be suitable for the calculation of a first decelerationset-point.

[0041] As described above, a deceleration set-point is determined on thebasis of the parameters X and V, and more specifically, on the basis ofthe parameters X_(final)−X and V_(final)−V.

[0042] According to the invention, the deceleration set-point is notapplied immediately but after a certain time.

[0043]FIG. 2 shows the representation of the variation of thedeceleration set-point which would be obtained by applying the methodaccording to the invention only once after an aircraft has touched thelanding strip.

[0044] The Y-axis shows the deceleration set-point Γ, which corresponds,for example, to a braking torque applied to the wheels of the landinggear. In addition, the Y-axis coincides with a time origin, taken, forexample, at impact of the aircraft on the strip.

[0045] Firstly, a minimum braking torque, referred to as Γ_(min), isapplied to the wheels. Γ_(min) may be, depending on the case, a lowset-point value, possibly zero, or, in the case of an iterative use ofthe method, a value corresponding to a previously defined decelerationset-point.

[0046] After a delay interval, at a time t_(c), the decelerationset-point is modified. A new braking torque Γ_(c) is applied to wheels.The value Γ_(c) is defined as a function of the previously acquiredposition and speed parameters, such that the desired final speed can bereached at the level of the exit point 16 a of the landing strip.

[0047] The calculation of the necessary deceleration may be carried out,for example, on the basis of movement equations according to thefollowing general formula:

V _(final) =a.t+V, and

X _(final) =X+V.t+a/2.t ²

[0048] In these equations, a represents deceleration and t time.Depending on the case, the time must be counted from the modification ofthe deceleration set-point, accounting for, if applicable, anydeceleration prior to the set-point modification time.

[0049] According to more complex models, the calculation of thedeceleration may account for other parameters such as characteristicfriction coefficients of the surface condition of the landing strip, thelift, etc.

[0050] Finally, according to another further possibility, which will bedescribed in more detail hereafter, the delay interval and thedeceleration set-point may be defined by a neural network computeraccounting for prior parameter learning.

[0051]FIG. 2 corresponds to an example of a particularly simplifiedembodiment of the invention wherein only two deceleration set-pointsΓ_(min) and Γ_(c) are taken into consideration. As can also be seenhereafter, an iterative or continuous embodiment of the method makes itpossible to readjust the deceleration set-point several times, or evencontinuously.

[0052]FIG. 3 shows, in the form of a graph, the variation of the speedof an aircraft landing on the landing strip and to which thedeceleration set-points in FIG. 2 are applied. The Y-axis which givesthe speed V as a function of time also coincides with the impact time,in the example described.

[0053] It can be seen that, between the impact time and the decelerationset-point modification time t_(c), the speed only falls slowly.

[0054] Indeed, up to the time t_(c), the aircraft only undergoesaerodynamic braking and, at the very most, very weak braking on thewheels.

[0055] However, from the time t_(c), the aircraft undergoes adeceleration a due to the braking torque Γ_(c).

[0056] If V₀ is taken to be the speed of the aircraft at the time t_(c),said speed will decrease roughly according to the equation mentionedabove, or more specifically:

V=V ₀ −a.(t−t _(c)).

[0057] The braking set-point is such that the final speed V_(final) isreached at the level of the strip exit junction.

[0058] It can be seen in FIG. 3 that, the later t_(c) is, the shorterthe taxiing time of the aircraft on the strip will be, due to its highspeed. However, this results in a greater deceleration. To this end, thedeceleration set-point calculation means may be controlled or programmedso as to define the time and deceleration value as a compromise betweenpassenger comfort requirements and strip occupation time reductionrequirements. The values also depend on the selected exit junction.

[0059] It is possible for example to prioritise late but highdecelerations when an airport is very congested and to apply moregradual and comfortable set-points in less busy situations.

[0060]FIG. 4, described below, shows, in block form, the main componentsof an item of braking equipment and illustrates a particular embodimentof the invention.

[0061] Reference 100 jointly refers to the aircraft and dynamic speedand position parameter acquisition means equipped therein. Theacquisition means are capable of continuously calculating particularlythe current position and current speed X and V mentioned above.

[0062] These parameters are sent to a neural network calculation unit102. It consists of, for example, a conventional neural network composedof three layers of cells operating according to a gradient backpropagation learning method.

[0063] The function of the neural network is to define the decelerationset-points and the modification times for said set-points. It may alsohave other additional functions. For example, in the approach phase,before landing, it may be used as a prediction tool to determine theexit junctions of the landing strip liable to be reached according tothe aircraft flying conditions (centring, weight, etc.), weatherconditions, and possibly the condition of the landing strip. Thetransmission of these parameters to the neural network is shown in FIG.4 in a simplified manner by an arrow.

[0064] The deceleration set-points produced by the computer 102 are sentto a braking system 104, which, in the example described, acts on thewheels of the main aircraft landing gear. More specifically, thedeceleration set-points are sent to the braking system via ananti-blocking system intended to prevent wheel blocking. Such ananti-blocking system is known to those skilled in the art and istherefore not described in detail here.

[0065] Finally, the braking system exerts on the wheels a braking torqueΓ as examined above with reference to FIG. 2.

[0066] An arrow F_(x) shows the action of the braking of the wheels onthe aircraft and particularly on the speed and position parameters. Anarrow F_(N), on the other hand, shows the dynamic action of the aircrafton the wheels (ground spoilers, aerodynamic behaviour, etc.).

[0067] A first retro-control can be carried out between the wheels 108of the landing gear and the braking system 106, by correcting thebraking torque as a function of wheel rotation speed and wheel rotationspeed variation data (Ω, dΩ/dt).

[0068] A second retro-control can be carried out between the aircrafttaxiing parameter acquisition system and the anti-blocking system 104.In this case, speed and acceleration data (V, dV/dt) is sent to theanti-blocking system.

[0069] Finally, the main retro-control can be carried out between theaircraft taxiing parameter acquisition systems and the neural networkcomputer 102. At any time, the new current position and speed valuesmake it possible to verify, by means of estimation, whether the finalspeed can actually be reached at the level of the selected strip exitjunction. If this is not the case, a new deceleration set-point may bedefined.

[0070] This retro-control may be continuous by continuously adjustingthe deceleration set-point, at the very least after the first set-pointmodification time.

[0071] Reference

[0072] (1) EP A 0 895 929.

1. System to control the deceleration of an aircraft during the taxiingphase on a landing strip, the system comprising: acquisition means (100)of the current position of the aircraft on the strip, acquisition means(100) of the current speed of the aircraft on the strip, characterisedin that it comprises: calculation means (102) of a decelerationset-point modification time (t_(c)), after the current time, and a newdeceleration set-point (Γc) to apply from said modification time, toreach the final position at the desired final speed, receiving positionand speed values from the acquisition means, and accounting for saiddesired final speed of the aircraft in said final position.
 2. Systemaccording to claim 1, comprising continuous acquisition means of thecurrent position and current speed of the aircraft, and continuouscalculation means of a new deceleration value.
 3. System according toclaim 1, wherein the current position acquisition means comprise a GPS(global positioning system) type system.
 4. System according to claim 1,wherein the current speed acquisition means comprise an IRS (internalreference system) type speed measurement system specific to theaircraft.
 5. System according to claim 1, wherein the calculation means(102) comprise a neural network computer.
 6. Braking equipment for anaircraft equipped with a control system according to claim
 1. 7. Brakingequipment according to claim 6, comprising an anti-blocking system (104)connected between the calculation means (102) and a wheel braking system(106) on the aircraft.
 8. Method to control the deceleration of anaircraft running on a landing strip, between at least a current positionof the aircraft occupied at a current time, at which said aircraft has acurrent speed, and a final position at which the aircraft must have adetermined final position, characterised in that a decelerationset-point modification time, after the current time, and a newdeceleration set-point applied from said set-point modification time,are determined as a function of the current position, the current speedand the final speed, in order to reach the final position at thedetermined speed.
 9. Method according to claim 8, wherein the currentposition and speed of the aircraft are measured continuously, andwherein a new deceleration value is defined continuously.
 10. Methodaccording to claim 9, wherein a deceleration modification time is alsodefined, when the deceleration set-point is not yet applied.